The present invention relates to electrographic recording. More particularly, it relates to an improved means and method for controlling the toner supply for such recording.
In the above-identified copending application of Roger D. Erickson, there has been disclosed an electrographic recording system which includes means wherein toner powder having electrical and magnetic properties is carried from a hopper to a recording station by a rotatable drum or shell. The shell is rotated about a magnetic core structure which produces a magnetic field to hold the toner powder onto the surface of the shell as it rotates. At the recording station, a dynamic bridge of the toner powder is formed between the periphery of the drum or shell and a magnetically permeable member positioned a predetermined distance from the surface of the drum or shell. A record member is driven along a path between the drum and the permeable member with the reverse side of the record member in contact with the permeable member. An array of recording electrodes are positioned to be in electrical contact with the toner powder in the bridge. The record member is backed up by a platen member at least a portion of which is electrically conductive. When one or more of the electrodes is energized, a conductive path is established from the electrode, through the bridge, to the surface of the recording member and the conductive back-up platen, electrically charging the dielectric surface of a recording member to deposit toner powder thereon.
In the system described in the above-mentioned copending application of Roger D. Erickson, the toner bridge is defined by the magnetic field established between the magnetic core about which the drum or shell rotates and the fixed magnetically permeable member. It has been found that, under certain circumstances, it is desirable to be able to modify the definition of the toner bridge in accordance with varying needs.